I install SyncThing-fork first of all.
SyncThing has all my music, notes, and books. Basically anything small enough that I don't worry about storage space lives in a sync folder, unless it's code in a report.
My personal use of tech is pretty heavily influenced by that app. If it weren't available I'd probably do a lot of things differently, and rely more on apps with usually proprietary sync built-in.
Then I get F-Droid, KDE connect, and BitWarden.
After that I usually customize the shortcuts in the tray. I'll get rid of the Bluetooth and location buttons so I can't accidentally turn them off, since I basically never purposely turn them off.
Then I get the do not disturb timer app, and get rid of the regular do not disturb, so I don't accidentally leave it on(It's very easy to forget when you only use it a few times a year at the absolute most).
Then I get all the usual proprietary "you are the product apps" and set them up, and install all the various apps I like having around.